The present invention relates to a butadiene copolymer, and more particularly to a butadiene copolymer suitable for use in tires, which is remarkably improved in processability with keeping resilience, wet grip property, abrasion resistance and mechanical properties on high levels.
A rubber well known as a rubber for tires is an emulsion styrene-butadiene copolymer prepared by an emulsion polymerization. However, this copolymer has the disadvantage of being poor in resilience and, therefore, it is not preferable from the viewpoint of energy saving.
Natural rubber, polyisoprene rubber and high-cis polybutadiene rubber are known as rubbers having a good resilience. However, these rubbers are poor in wet grip property, and accordingly are not preferable from the viewpoint of running stability on wet roads.
As a rubber having both good resilience and good wet grip property, there is known a rubber prepared by polymerizing butadiene alone, or butadiene and styrene, in a hydrocarbon solvent in the presence of an organolithium compound as the polymerization initiator and a Lewis base such as an ether compound or a tertiary amine as an agent for controlling microstructure. However, this rubber has the deficiency that the processability is insufficient. In order to improve the processability, it is also proposed to convert the polymer into a branched polymer by acting a tri- or tetrafunctional coupling agent on the active ends of the polymer. However, the processability is not sufficiently improved even by this method. In particular, in case of processing the rubber by a method using a large amount of a filler which is adopted in producing automobile tires superior in high speed running characteristics, the processability is unsatisfactory.
Abrasion resistance and mechanical properties are also required as the characteristics of rubbers for tire use in addition to the above-mentioned resilience, wet grip property and processability. However, any rubber which satisfies all of these characteristics, has not been proposed.
It is an object of the present invention to provide a rubber suitable for use in tires and having excellent general characteristics required for tire use.
A further object of the present invention is to provide a butadiene copolymer suitable as a tire rubber, which is remarkably improved in processability with keeping resilience, wet grip property, abrasion resistance and mechanical properties on high levels.
A still further object of the present invention is to provide a process for preparing the above-mentioned butadiene copolymer.
Another object of the present invention is to provide a rubber composition suitable for producing tires such as automobile tires and having an excellent processability.
A still another object of the present invention is to provide a tire having excellent characteristics such as resilience, wet grip property, abrasion resistance and mechanical properties.
These and other objects of the present invention will become apparent from the description hereinafter.